The present invention concerns a heat exchanger for the cooling of hot gases, particularly from the synthesis of ammonia.
In known heat exchangers (DE-PS No. 20 07 528, DE-OS No. 30 49 409), evaporating water is employed exclusively as cooling medium for the cooling of the hot gases leaving an ammonia converter. This has the consequence that the gases cannot be cooled below the boiling point of the water. If lower temperatures are required, then the gases would have to be fed to a further heat exchanger, in which colder water flows around the gas-conducting heat exchanger tubes.
In order to set a certain final temperature of the cooled gases, it is, furthermore, known to admix a partial current of the hot gases to the already cooled gases. In a known heat exchanger (DE-PS No. 28 46 455), the partial current is conducted through a tube lying parallel with the heat exchanger tubes out of the gas entry chamber into the gas exit chamber. For the regulation of the partial quantity, the exit end of the tube is closable with the aid of a throttle cone.
Furthermore, a tube bundle steam generator is known (DE-OS No. 24 08 099), in which a part of the tubes is enclosed by a preheater shell. The feed stub for the water to be evaporated is led through the preheater shell. The preheater shell is connected with the tube plate at its one end and open at its other end.
The known tube bundle steam generator with built-in preheater zone can preheat only exactly as much water as is also evaporated. This is a disadvantage, because preheated water from the gas cooler is utilized also for other steam generators in ammonia plants. The separate arrangement of preheater and evaporator as gas cooler for ammonia plants is very expensive, since the equipment because of the high pressure of the gases require a great wall thickness for the housings.